Flushes the buffer of incoming serial data. Any call to Serial.read() or Serial.available() will return only data received after all the most recent call to Serial.flush().
Serial.flush() waits for outgoing data to transmit before clearing the buffer contents.
flush() inherits from the Stream utility class.
Serial.flush()
Arduino Mega only:
Serial1.flush()
Serial2.flush()
Serial3.flush()
none
nothing